Porous films by backfilling with reactive compounds

Abstract

The invention provides methods for modifying one or more properties of porous thin films. In such methods, a formulation comprising a reactive species is applied to the porous thin film and allowed to crosslink. In some embodiments, the crosslinked network thus formed imparts increased mechanical strength and wear resistance to the porous thin films.

1. A method for modifying a property of a porous thin layer-by-layer (LbL) film less than 10 μm thick, disposed on a substrate, and comprising an inorganic material in the form of charged nanoparticles, a polymer polyelectrolyte, and an interconnected network of open pores filled with ambient gas, the method comprising:
 applying a filling solution comprising a reactive species and optionally a solvent to the surface of the film; 
 allowing the filling solution to remain in contact with the surface of the film for a period of time between 5 seconds and 1 hour and sufficient to allow the reactive species to be imbibed into the pores; 
 removing excess filling solution from the surface of the film; and thereafter 
 crosslinking the reactive species imbibed in the pores to form a crosslinked network within the pores. 
 
     
     
       2. The method of  claim 1  wherein the crosslinking is effected by applying a crosslinking stimulus to the film sufficient to cause initiation of crosslinking, and the stimulus is heat. 
     
     
       3. The method of  claim 1  wherein the crosslinking is effected by allowing sufficient time for auto-initiation of crosslinking. 
     
     
       4. The method of  claim 1  wherein the excess filling solution is removed with a stream of gas. 
     
     
       5. The method of  claim 1 , wherein the inorganic material is selected from metal oxides, metal nitrides, metal sulfides, metals, quantum dots, graphene, carbon nanotubes, and combinations thereof. 
     
     
       6. The method of  claim 1 , wherein the inorganic material is a metal oxide selected from titanium dioxide, silicon dioxide, cerium dioxide, tin oxide and zirconium oxide. 
     
     
       7. The method of  claim 1 , wherein the polyelectrolyte is selected from poly(diallyldimethylammonium chloride) (PDAC), poly(allylamine hydrochloride (PAH), poly(sulfonated styrene) (PSS), poly(acrylic acid) (PAA), poly(ethylene imine), poly(vinyl alcohol), poly(ethylene oxide), polythiophenes, and copolymers thereof. 
     
     
       8. The method of  claim 1  wherein the polyelectrolyte is a biologically derived polyelectrolyte selected from chitosan, carboxymethylcellulose, polysaccharides, hyaluronic acid, and copolymers thereof. 
     
     
       9. The method of  claim 1 , wherein the reactive species is an orthosilicate selected from tetramethyl orthosilicate (TMOS), tetraethyl orthosilicate (TEOS), and tetrapropyl orthosilicate. 
     
     
       10. The method of  claim 1  wherein the reactive species is a crosslinkable acrylate selected from 2-hydroxyethyl acrylate (HEA), pentaerythritol triacrylate (PETA), 2-hydroxyethyl methacrylate (HEMA), trimethylolpropane triacrylate (TMPTA), and 1,6-hexandiol diacrylate (HDDA). 
     
     
       11. The method of  claim 1  wherein the inorganic material is silicon dioxide or titanium dioxide, the polyelectrolyte is poly(diallyldimethylammonium chloride) (PDAC), and the reactive species is tetraethyl orthosilicate (TEOS). 
     
     
       12. The method of  claim 1  wherein the period of time is less than 5 minutes. 
     
     
       13. The method of  claim 1 , wherein the filling solution has a pH below 2.0. 
     
     
       14. The method of  claim 1  wherein the filling solution is applied by spraying the filling solution onto the surface of the film. 
     
     
       15. The method of  claim 1  wherein the substrate is glass or plastic. 
     
     
       16. The method of  claim 1  wherein the inorganic material is silicon dioxide or titanium dioxide, the polyelectrolyte is poly(diallyldimethylammonium chloride) (PDAC), the reactive species is tetraethyl orthosilicate (TEOS), the excess filling solution is removed with a stream of gas, the period of time is less than 5 minutes, the filling solution has a pH below 2.0, and the crosslinking stimulus is applied to the film, the stimulus is heat. 
     
     
       17. The method of  claim 1  further comprising prior to applying the filling solution heating the film to a temperature sufficient to pyrolyze the polyelectrolyte, but insufficient to sinter the inorganic material. 
     
     
       18. The method of  claim 17  wherein the crosslinking is effected by applying a crosslinking stimulus to the film sufficient to cause initiation of crosslinking, and the stimulus is heat. 
     
     
       19. The method of  claim 17  wherein the excess filling solution is removed with a stream of gas. 
     
     
       20. The method of  claim 17 , wherein the inorganic material is a metal oxide selected from titanium dioxide, silicon dioxide, cerium dioxide, tin oxide and zirconium oxide. 
     
     
       21. The method of  claim 17 , wherein the polyelectrolyte is selected from poly(diallyldimethylammonium chloride) (PDAC), poly(allylamine hydrochloride (PAH), poly(sulfonated styrene) (PSS), poly(acrylic acid) (PAA), poly(ethylene imine), poly(vinyl alcohol), poly(ethylene oxide), polythiophenes, Nafion, and copolymers thereof. 
     
     
       22. The method of  claim 17 , wherein the reactive species is an orthosilicate selected from tetramethyl orthosilicate (TMOS), tetraethyl orthosilicate (TEOS), and tetrapropyl orthosilicate. 
     
     
       23. The method of  claim 17  wherein the inorganic material is silicon dioxide or titanium dioxide, the polyelectrolyte is poly(diallyldimethylammonium chloride) (PDAC), and the reactive species is tetraethyl orthosilicate (TEOS). 
     
     
       24. The method of  claim 17  wherein the inorganic material is silicon dioxide or titanium dioxide, the polyelectrolyte is poly(diallyldimethylammonium chloride) (PDAC), the reactive species is tetraethyl orthosilicate (TEOS), the excess filling solution is removed with a stream of gas, the period of time is less than 5 minutes, the filling solution has a pH below 2.0, the crosslinking stimulus is applied to the film, and the stimulus is heat.